Is there a way to get watch to update the screen when the command succeeds? I have a command that infrequently succeeds, and I want it to show the last successful output.
Is there a way without a helper program?
watch does not allow to conditionally show the output of a command, but you can start your command from script and show its output depending on the termination status. Use something like this:
#!/bin/bash
cmd > /tmp/cmd_out
if [ $? -eq 0 ]; then
cat /tmp/cmd_out
fi
Of course, your command should return proper exit status (not just 0 in any case) or this method will not work.
Related
I am writing a script in bash and I have some 15+ kubectl commands, after execution of each kubectl command, I need to check if echo $? is zero (or) not(which means it is successfully executed or not), if it is not zero, then I should exit from the script without executing the further lines/ further commands/further functions specified in the script. For this, I wrote a function, after every command I am calling this function to do the condition check of echo $? (for this function I am passing echo $? as an argument).
how to exit completely from the script once the echo $? !=0?
I'm sorry but your script doesn't make much sense to me, i'll try to provide an answer to your question anyway.
In bash scripting exit code 0 means success, anything but that means an error with some numbers having a special meaning.
To achieve what you want to do you need this simple function to be executed after every kubectl command:
function check() {
[ $? != 0 ] || exit 1
}
$command
check
Is it possible to trap error (unknown command) from the CLI, and do something in the case an error occured ?
To be more precise, I search a way to do something like this:
if [ previousCommandFails ] ; then
echo lastCommand >> somewhere.txt
fi
Echo is just an example to say that I need to access this lastCommand.
I want it to be a default behaviour in my computer, so the code must be placed somewhere like ~/.bashrc.
You can try the following solution. I don't guarantee that it's a good solution but it may help with your case.
Create a small script which can test the previous command i.e. test.sh with content:
if [ $? -ne 0 ]
then
history 1 >> /path/to/failed_commands.txt
fi
Then set this variable:
PROMPT_COMMAND+="source /path/to/test.sh"
PROMPT_COMMAND If set, the value is executed as a command prior to
issuing each primary prompt.
It depends on what you call fail. If it is just returning a non 0 value, I am afraid that you have to explicitely test it after each command, or use a specialized shell (*).
But trap can be used to execute a specific command when a signal is received:
trap action signal
If this is not enough, you will have to get the source of a shell (posix shell or bash) and tweak it for meet you needs...
I am writing shell script to install my application. I have more number of commands in my script such as copy, unzip, move, if and so on. I want to know the error if any of the commands fails. Also I don't want to send exit codes other than zero.
Order of script installation(root-file.sh):-
./script-to-install-mongodb
./script-to-install-jdk8
./script-to-install-myapplicaiton
Sample script file:-
cp sourceDir destinationDir
unzip filename
if [ true]
// success code
if
I want to know by using variable or any message if any of my scripts command failed in root-file.sh.
I don't want to write code to check every command status. Sometimes cp or mv command may fail due to invalid directory. At the end of script execution, I want to know all commands were executed successfully or error in it?
Is there a way to do it?
Note: I am using shell script not bash
/* the status of your last command stores in special variable $?, you can define variable for $? doing export var=$? */
unzip filename
export unzipStatus=$?
./script1.sh
export script1Status=$?
if [ !["$unzipStatus" || "$script1Status"]]
then
echo "Everything successful!"
else
echo "unsuccessful"
fi
Well as you are using shell script to achieve this there's not much external tooling. So the default $? should be of help. You may want to check for retrieval value in between the script. The code will look like this:
./script_1
retval=$?
if $retval==0; then
echo "script_1 successfully executed ..."
continue
else;
echo "script_1 failed with error exit code !"
break
fi
./script_2
Lemme know if this added any value to your scenario.
Exception handling in linux shell scripting can be done as follows
command || fallback_command
If you have multiple commands then you can do
(command_one && command_two) || fallback_command
Here fallback_command can be an echo or log details in a file etc.
I don't know if you have tried putting set -x on top of your script to see detailed execution.
Want to give my 2 cents here. Run your shell like this
sh root-file.sh 2> errors.txt
grep patterns from errors.txt
grep -e "root-file.sh: line" -e "script-to-install-mongodb.sh: line" -e "script-to-install-jdk8.sh: line" -e "script-to-install-myapplicaiton.sh: line" errors.txt
Output of above grep command will display commands which had errors in it along with line no. Let say output is:-
test.sh: line 8: file3: Permission denied
You can just go and check line no.(here it is 8) which had issue. refer this go to line no. in vi.
or this can also be automated: grep specific line from your shell script. grep line with had issue here it is 8.
head -8 test1.sh |tail -1
hope it helps.
I'm running a command inside a gnome-terminal like this:
gnome-terminal --disable-factory -x bash -c "<some_command>"
if i then check the pass/fail status of the last command using $? i always get 0, even if <some_command> fails.
Is there a way to reflect the pass/fail status of <some_command> to the original shell so $? will show the correct result?
This is not really possible because even with appending exit $? to the command, bash is a subprocess of gnome-terminal which is a subprocess of your shell session.
Even if gnome-terminal's subprocess (bash) exits abnormally, gnome-terminal's GTK+ UI process still exits normally with 0.
This sounds like an X/Y Problem -- rather than using gnome-terminal and checking the exit status, which is weird and convoluted, find the root of the problem you want to solve and chase that instead.
Below is my script that I am executing in the bash. And it works fine.
fileexist=0
for i in $( ls /data/read-only/clv/daily/Finished-HADOOP_EXPORT_&processDate#.done); do
mv /data/read-only/clv/daily/Finished-HADOOP_EXPORT_&processDate#.done /data/read-only/clv/daily/archieve-wip/
fileexist=1
done
Problem Statement:-
In my above shell script which has to be run daily using cron job, I don't have any error/exception handling mechanism. Suppose if anything gets wrong then I don't know what's has happened?
As after the above script is executed, there are some other scripts that will be dependent on the data provided by above script, so I always get's complaint from the other people who are depending on my script data that something wrong has happened.
So is there any way I can get notified if anything wrong has happened in my script? Suppose if the cluster is having some maintenance and at that time I am running my script, so definitely it will be failing for sure, so can I be notified if my above scripts failed, so that I will be sure something wrong has happened.
Hope my question is clear enough.
Any thoughts will be appreciated.
You can check for the exit status of each command, as freetx answered, but this is manual error checking rather than exception handling. The standard way to get the equivalent of exception handling in sh is to start the script with set -e. That tells sh to exit with a non-zero status as soon as any executed command fails (i.e. exits with a non-zero exit status).
If it is intended for some command in such a script to (possibly) fail, you can use the construct COMMAND || true, which will force a zero exit status for that expression. For example:
#!/bin/sh
# if any of the following fails, the script fails
set -e
mkdir -p destdir/1/2
mv foo destdir/1/2
touch /done || true # allowed to fail
Another way to ensure that you are notified when things go wrong in a script invoked by cron is to adhere to the Unix convention of printing nothing unless an error ocurred. Successful runs will then pass without notice, and unsuccessful runs will cause the cron daemon to notify you of the error via email. Note that local mail delivery must be correctly configured on your system for this to work.
Its customary for every unix command line utility to return 0 upon success and non-zero on failure. Therefore you can use the $? pattern to display the last return value and handle things accordingly.
For instance:
> ls
> file1 file2
> echo $?
> 0
> ls file.no.exist
> echo $?
> 1
Therefore, you can use this as rudimentary error detection to see if something goes wrong. So the normal approach would be
some_command
if [ $? -gt 0 ]
then
handle_error here
fi
well if other scripts are on the same machine, then you could do a pgrep in other scripts for this script if found to sleep for a while and try other scripts later rechecking process is gone.
If script is on another machine or even local the other method is to produce a temp file on remote machine accessible via a running http browser that other scripts can check status i.e. running or complete
You could also either wrap script around another that looks for these errors and emails you if it finds it if not sends result as per normal to who ever
go=0;
function check_running() {
running=`pgrep -f your_script.sh|wc -l `
if [ $running -gt 1 ]; then
echo "already running $0 -- instances found $running ";
go=1;
}
check_running;
if [ $go -ge 1 ];then
execute your other script
else
sleep 120;
check_running;
fi